Fogged direct positive silver halide element containing a selenium compound sensitizer

ABSTRACT

Direct-positive photographic elements are described which comprise uniformly fogged radiation-sensitive silver halide and a selenium compound of the formula : R - Se - Q wherein R is alkyl, aralkyl, alkaryl, aryl or a heterocyclic ring system and Q represents -Se-R&#39;&#39; or -S-R&#39;&#39; wherein R&#39;&#39; has one of the significances given for R, halogen, cyano, or WHEREIN EACH OF R1, R2 and R3 is alkyl, aralkyl or aryl and X is an anion but does not exist when R itself contains an anionic group. The selenium compounds increase the speed of the directpositive silver halide elements.

United States Patent 1 1 Florens et al.

[54] FOGGED DIRECT POSITIVE SILVER HALIDE ELEMENT CONTAINING A SELENIUMCOMPOUND SENSITIZER [75] Inventors: Raymond Leopold Florens, Edegem;Robert Joseph Pollet, Vremde,

both of Belgium [73] Assignee: Gevaert-Agfa N.V., Mortsel, Belgi- [22]Filed: Feb. 18, 1971 211 App]. No.2 116,661

[30] Foreign Application Priority Data 1 1 Feb. 20, 1973 PrimaryExaminer-J. Travis Brown Assistant Examiner-Won l-l. Louie, Jr.Attorney-Brufsky, Staas, Breiner & Halsey [57] ABSTRACT Direct-positivephotographic elements are described which comprise uniformly foggedradiation-sensitive silver halide and a selenium compound of the formulaR Se Q wherein R is alkyl, aralkyl, alkaryl, aryl or a heterocyclic ringsystem and Q represents Se-R' or S-R' wherein R has one of thesignificances given for R, halogen, cyano, or

wherein each of R R and R is alkyl, aralkyl or aryl and X- is an anionbut does not exist when R itself contains an anionic group. The seleniumcompounds increase thespeed of the direct-positive silver halideelements. 4

17 Claims, No Drawings FOGGED DIRECT POSITIVE SILVER IIALIDE ELEMENTCONTAINING A SELENIUM COMPOUND SENSITIZER The present invention relatesto radiation sensitive direct-positive silver halide emulsions, moreparticularly to direct-positive emulsions having an improvedradiation-sensitivity.

It is known that positive photographic images can be obtained withoutpreviously forming a negative silver image by the use of silver halideemulsions that have been pre-fogged by overall exposure to actinicradiation or by overall chemically fogging with reducing substances.Upon image-wise exposure of the pre-fogged emulsions the developmentcenters formed by said fogging are destroyed at the exposed areas andremain at the unexposed areas. By subsequent development by means ofsilver halide developers a direct-positive image is obtained.

The image-wise exposure of the pre-fogged silver halide emulsion, whichresults in an image-wise destruction of the development specks, can beaccomplished for instance by utilizing the solarization effect or theHerschel-effect. Solarization is a reversal phenomenon which is producedby over-exposure of a silver halide emulsion wherein a uniform latentimage corresponding to the critical exposure has been formed byprefogging, said over-exposure resulting in a destruction of thedevelopment centers.

According to the Herschel-effect a latent image can be reversed by asecond exposure to red or infra-red light. The sensitive layer is firstfogged uniformly to its maximum density with blue-violet light or bychemical means for example reducing agents and is then imagewise exposedwith light of long wavelength, preferably at low intensity and for along time. The Herschel-effect may, however, also be obtained with lightof shorter wavelength such as yellow light if the photographic materialhas been treated with so-called desensitizing dyes.

From the foregoing it is clear that the production of direct-positiveimages can proceed according to two different techniques. In bothprocesses an increase in sensitivity is pursued.

It has now been found that the speed of direct-positive elements can beincreased by incorporating into said elements a selenium compoundcorresponding to the following general formula:

R Se Q wherein:

R stands for an alkyl, aralkyl, alkaryl, aryl or heterocyclic groupwhich groups may carry substituents for example halogen, e.g. chlorineand bromine, carboxyl, sulpho, nitro, amino, substituted amino,acylamino e.g. acetamide, carbamoyl, etc.,

or form part of a heterocyclic ring system, and

Q stands for an electron-withdrawing group or atom with strong leavingproperties for example the group --Se-R' or S-R' wherein R has the samesignificance as R, halogen,

wherein each of R R and R stands for alkyl, aralkyl or aryl and X standsfor an anion but does not exist when R itself contains an anionic group.

Therefore, in accordance with the present invention a direct-positivephotographic silver halide element is provided comprisingradiation-sensitive silver halide, which has been uniformly fogged, anda selenium compound as defined above.

The present invention further provides a method of producingdirect-positive images which comprises image-wise exposing adirect-positive element having prefogged silver halide and comprising aselenium compound as defined above, and developing said element in asilver halide developing solution.

The selenium compounds corresponding to the above general formula areespecially suitable for increasing the sensitivity of direct-positiveemulsions designed to exhibit the solarization technique. However, itwas found that they also promote reversal by the Herschel effect.

The direct-positive emulsions can be prepared according to knownmethods. The silver halide composition is not critical and may consistof silver chloride, silver bromide, silver iodide or mixtures thereof.

As is known, fogging of the emulsions may occur by means of an overalluniform exposure to actinic radiation or by means of chemically foggingagents e.g. by means of reducing agents such as hydrazine,hydroxylamine, formaldehyde, tin(ll)chloride, thiourea dioxide alsocalled formamidine sulphinic acid, etc.

In addition to the light-sensitive silver halide, the direct-positiveemulsions may comprise all kinds of other known emulsion ingredients forinstance compounds of metals that are more electro-positive than silversuch as compounds of gold, platinum, palladium and iridium for examplegold(lll) chloride, potassium chloroaurate and (NH,) PdCl.,, wettingagents, development accelerators, optical brightening agents, hardeners,stabilizers, electron-accepting compounds for example the knowndesensitizing dyes for directpositive emulsions, etc.

Representative examples of selenium' compounds which correspond to theabove general formula and which have been found particularly suitablefor increasing the reversal speed of direct-positive radiationsensitivesilver halide elements are those listed below. They can be preparedaccording to the methods described in the literature referred or asdescribed hereinafter.

Ber. 25, 3,048 (1892).

23--- Q-smm Ben, 92, 40 (1959).

J. Chem. 800., 1,364 (1926).

J. Chem. 80m, 1,364 (1926).

J. Chem. Sum, 2,831 (1952).

J. Chem. Soc, 2,280 (1928).

Houben-Weyl Methoden der organischen Chemic Band XI Bull. Soc. Chim.,245 (1950).

Acta Chum. Scand. 17, 268 (1963) Arklv. Kmnl, .20, 1163 (HIM). AclvnChem. HcmuL, 21, 837 (1W7).

Houben-Weyl Muthodcn der organlschen Chemio"-Selen Ber. 65, 812 (1932).

J. Chem. 800., 1,648 (1926).

Ber. 66, 708 (1933).

J. Chem. 500., 1,648 (1926).

Ben, 46, 92 1913 Compound 3 was prepared by dissolving 158 g of compound5, prepared as described below, in 400 ml of acetic acid with heatingand then pouring the reaction mixture into a mixture of 1,800 ml ofconcentrated hydrochloric acid and 900 ml of water. The mixture wasstirred and refluxed for 12 hours. Upon cooling, the benzoic acid formedwas filtered off by suction and the filtrate concentrated byevaporation. The yellow residue was recrystallized from 90 percentmethanol. Melting point: 182C.

Compound 5 was prepared by dissolving 0.5 mole of bromoethyl-benzamidein 300 ml of methanol and treating the solution while stirring with asolution of 0.55 mole of KSeCN in 300 ml of methanol. The mixture wasrefluxed for 30 minutes and cooled, whereupon the potassium bromide wasfiltered off by suction and the filtrate treated with 91 g of potassiumhydroxide. Then, 300 ml of ice-water was added and the yellowprecipitate collected after washing with methanol/water (1:1) and ether.Melting point 158C.

Compound 6 was prepared by treating 1 mole of freshly prepared Na Se inaqueous solution with 1 m kqr lsh q dissolve! 193 29291? 8 Afterextraction with ether, drying the either extract and concentrating theextract by evaporation compound 6 having a melting point of 9 1C wasobtained.

Compound 1 l was prepared as follows:

To 0.5 mole of meta-chlorobromobenzene in 500 ml of ether, 12 g ofmagnesium and 0.5 mole of selenium were added. The mixture was stirredfor a few hours whereupon it was poured into ice-water in the presenceof 75 ml of hydrochloric acid. The ether layer was separated and driedwhereupon an air-current was bubbled through the ether layer. Afterevaporation of the ether, the residual oil was distilled. Boiling point:208-21 1C/2.5 mm.

Compound 19 was prepared as follows: 28.8 g (0.2 mole) of potassiumselenocyanate were dissolved in 75 ml of water whereupon a solution wasadded, with stirring, of 24.4 g (0.2 mole) of propane sultone in 75 mlof alcohol. The mixture was refluxed for 15 min., filtered andconcentrated by evaporation. The residue was recrystallized fromethanol/water (l/ 1). Melting point: 258C.

Compound 27 was prepared as follows Twenty-two g of2-methyl-6-amino-benzothiazole in 80 ml of N hydrochloric acid and 400ml of water were diazotized at 0C with a solution of g of sodium nitritein 20 ml of water whereupon the solution was buffered to pH 4 by meansof 75 g of sodium acetate. A solution of 28.8 g of potassiumselenocyanate in 50 ml of water was added and the precipitate formed wasfiltered by suction. The product was recrystallized from ethylene glycolmonomethyl ether. Melting point: 137C.

Compound 28 was prepared as follows: 0.05 mole of tributylphosphineselenide and 0.1 mole of propane sultone were heated for 30 minutes onan oil bath of 100C. The oil obtained was treated with ether andsolution was treated, after having been cooled, with ether whereupon thewhite precipitate formed was washed with ether and dried. Thetriphenylphosphine selenide used in the preparation of compound 29 wasfound itself to have a speed-increasing effect in directpositiveemulsions as described in the present invention.

The selenium compounds of use according to the invention may be used inamounts varying between very wide limits. The optimum amounts can bereadily determined by trial. Generally they are used in amounts between1 and mg per mole of silver halide. They are added to thedirect-positive silver halide emulsion preferably just before coating ona suitable support.

The selenium compounds as defined above are particularly suitable foruse in direct-positive emulsions containing in the interior of thesilver halide grains, centers promoting the deposition of photolyticsilver.

Photographic emulsions comprising in the interior of the silver halidegrains, centers promoting the deposition of photolytic silver are known,for instance, from United Kingdom pat. specification Nos. 1,011,062,1,027,146 and 1,151,781.

According to United Kingdom Pat. specification No. 1,011,062 emulsionshaving ripening nuclei in the interior of the grains are prepared byadmixture of a coarse-grained silver halide emulsion, which has beenchemically ripened and comprises ripening nuclei at the surface of thegrains, with a fine-grain, silver halide emulsion followed by physicalripening of the mixture whereby the large grains grow at the cost of thesmall grains so that the unripened fine-grain emulsion deposits aroundthe ripened coarse-grain emulsion.

In United Kingdom Pat. specification No. 1,027,146 a process has beendescribed and claimed according to which silver halide emulsions areprepared having a narrow grain-size distribution and containingcomposite silver halide granules of which the internal structure isdifferent from the surface structure. According to one embodiment ofthis process a fine-grained silver halide emulsion withnarrow-grain-size distribution is prepared first whereupon theprecipitation of the silver halide is interrupted and the surface of thesilver halide nuclei is chemically or physically modified eg bytreatment with reducing agents such as hydrazine and derivatives,ascorbic acid and formaldehyde, by treatment with noble metal salts suchas gold salts or by exposure to actinic radiation, and finallyprecipitation of the same or another silver halide is continued.

By fogging the emulsions formed according to these United Kingdom Pat.specifications Nos. 1,011,062 and 1,027,146 before or after coating on asupport, a photographic direct-positive silver halide emulsion can beobtained.

According to United Kingdom Pat. specification No. 1,151,781 there isprovided a method of making a photographic direct-positive materialwhich comprises forming grains of a first light-sensitive silver salt,treating these grains so as to produce in them centers which promote thedeposition of photolytic silver, covering the treated grains with alayer of a second light-sensitive silver salt and fogging the resultingemulsion before or after coating on a support.

Further details as regards the preparation of Directpositive silverhalide emulsions having in the interior of the silver halide grainscenters promoting the deposition of photolytic silver can be found inthe above United Kingdom Patent specifications.

In accordance with the present invention, directpositive silver halideemulsions containing in the interior of the silver halide grains centerspromoting the deposition of photolytic silver are preferably obtained bythe following steps l. the formation of silver halide grains mixing inan aqueous gelatin solution a dissolved water-soluble silver salt and adissolved water-soluble alkali metal halide salt,

2. the interruption of the precipitation,

3. treatment of the silver halide grains (cores) so as to producecenters which promote the deposition of photolytic silver,

4. the further mixing of silver salt and halide salt solutions thusforming a shell of silver halide around the cores, and

5. the fogging of the resulting silver halide emulsion at the surface ofthe silver halide grains to such an extent that after a sufficientimage-wise exposure of the emulsion layer to radiation to which thegrains are sensitive, a direct-positive silver image can be obtained bytreatment of the exposed emulsion in a silver halide developer.

In preparing suchlike direct-positive emulsions, the cores may betreated according to any of the known procedures for producing centerswhich promote the deposition of photolytic silver. Thus the cores may befogged by exposure to radiation or they may be chemically sensitized.The cores are preferably chemically sensitized and any of the usualprocedures may be used therefor. Thus the cores may be digested withnaturally active gelatin or with a labile sulphur compound. They arepreferably chemically sensitized with a gold or other noble metalsensitizer or with reduction sensitizers or with a mixture of both. Goldsensitization preferably occurs by means of a mixture of water-solublegold salts such as gold(lll)chloride, and thiocyanates forming complexeswith gold and having a solvent action on the silver halide grains e.g.alkalimetal and ammonium thiocyanates. The cores may also contain speedincreasing addenda such as quaternary ammonium compounds and compoundsof the polyethylene glycol type.

The precipitation of the silver halide is preferably carried out bysimultaneous addition of the halide salt solution and the silver saltsolution to the gelatin solution and keeping the pAg value as constantas possible during the precipitation.

The composite silver halide granules formed may contain silver chloride,silver bromide or silver iodide or mixtures thereof. For example, a coreof silver bromide can be coated with a layer of silver chloride or amixture of silver bromide and silver iodide, or a core of silverchloride can have deposited thereon a layer of silver bromide. However,the composite silver halide granules preferably have an interior core ofsilver bromide around which silver bromide has been deposited.

Gelatin is preferably used as vehicle for the composite silver halidegranules but like in other silver halide emulsions the gelatin may bewholly or partly replaced by other hydrophilic colloids, for examplecolloidal albumin, zein, agar-agar, polyvinyl alcohols, polyvinylacetals, hydrolyzed cellulose esters or ethers, etc.

In addition to the selenium compounds the directpositive silver halideemulsions comprising in the interior of the silver halide grains centerspromoting the deposition of photolytic silver may also comprise allkinds of known emulsion ingredients for direct-positive emulsions forexample wetting agents, development accelerators, optical brighteningagents, hardeners, stabilizers, electron-accepting compounds such as theknown desensitizing dyes for direct-positive emulsions, blue speedincreasing merocyanine dyes as described in United Kingdom Patentspecification No. 1,186,718, carbocyanine dyes, etc.

The emulsions containing in the interior of the silver halide grainscenters promoting the deposition of photolytic silver are uniformlyfogged at the surface of the grains. Fogging may occur by exposure ofthe emulsion, before or after coating, to actinic radiation, butpreferably chemical fogging is applied. The emulsion may be chemicallyfogged for instance, by sensitizing to fog using one of the chemicalsensitization methods outlined above. For this purpose reducing agents,eg

hydrazine, hydroxylamine, tin(Il) salts, such as stanno chloride,ascorbic acid, formaldehyde, thioureadioxide, etc. can be successfullyused.

According to a special embodiment of the present invention, the centerspromoting the deposition of photolytic silver in the interior of thesilver halide grains are produced by chemical sensitization with a goldcompound together with reduction sensitizer for example thiourea dioxidealso called formamidine sulphinic acid and derivatives thereof whereasthe external fogging of the composite silver halide granules occuts withthe same reduction sensitizer. The use of thiourea dioxide orformamidine sulphinic acid and derivatives thereof is known from UnitedKingdom Patent specification No. 789,823 and from US. Pat. Specs. Nos.2,983,609 and 2,983,610.

The emuisions of the invention can be coated on any of a wide variety ofsupports in accordance with usual practice to provide sensitivematerials of the invention. When these materials are exposed to an imageand thereafter developed in a conventional developer for example ap-monomethylaminophenol/hydroquinone developer a direct-positive silverimage is formed. This image can thereafter be fixed or stabilized byconventional techniques.

Direct-positive silver halide materials comprising selenium compounds ofthe above general formula and having centers promoting the deposition ofphotolytic silver in the interior of the silver halide grains preparedaccording to the processes described above by interrupted precipitationcan also be developed by means of so-called lith-developers, asdescribed in co-pending application No. 17, 162/69 in order to obtaindirectpositive images with very steep gradation curve. By alith-developer there is understood a developing composition forlight-exposed silver halide containing a bisulphite-addition compound ofan aliphatic aldehyde or ketone e.g. formaldehyde bisulphite, andhydroquinone as the sole developing agent.

The following examples illustrate the present invention.

EXAMPLE 1 A washed silver chloroiodide (99.65 mole percent of chlorideand 0.35 mole percent of iodide) emulsion comprising per kg an amount ofsilver halide equivalent to 75 g of silver nitrate was melted by heatingto 50C and the pH was adjusted to 7 by means of sodium hydroxide. Per kgof emulsion were added 20 ml of a 4 percent aqueous formaldehydesolution and 100 ml of a 0.1 percent aqueous solution of sodiumhydroxide. The emulsion was kept at 50C for 50 min. Thereupon the pH wasreduced to 6 by means of an aqueous solution of hydrogen chloride,whereupon 200 mg of the desensitizing compoundl-(2,4-dinitroanilino)-1,4- dihydro-4,4,6-trimethyl-2-pyrimidinethiolthe preparation of which is described in example 2 of the United KingdomPatent specification No. 796,873 were incorporated into the emulsion.

After addition of the necessary coating aids, the emulsion was dividedinto two aliquot portions A and B. Per kg of emulsion portion B 16 mg ofthe selenium compound 23 were added whereas to emulsion portion A noselenium compound was added. Both emulsions were then coated in asimilar way on a polyethylene terephthalate support and dried.

Both light-sensitive materials were exposed reflectographically througha grey test wedge, a yellow filter layer being applied to the back ofthe polyester base. During the exposure the emulsion layers stood incontact with an original containing white and black areas. The materialswere then developed for 120 sec. at 20C in a developing bath of thefollowing composition:

water (40C) 800 ml p-monomethylaminophenol sulphate 1.5 g anhydroussodium sulphite 25 g hydroquinone 6 g anhydrous sodium carbonate 40 gpotassium bromide l g water to make 1000 ml The sensitometric resultsobtained are listed in the table below.

The speed (S) is expressed on a percentage basis with respect to thereference emulsion A, the speed of TABLE Material D. -u: S

A 0.01 4.20 100 B 0.0 l 4.20 l l 8 EXAMPLE 2 Example 1 was repeated withthe only difference that development took place using a lith-developerhaving the following composition:

The sensitometric results obtained are listed in the table below.

Material D- D S EXAMPLE 3 ml of a 3N aqueous solution of potassiumbromide and 75 ml of a 3N aqueous solution of silver nitrate weresimultaneously introduced at a rate of 10 ml per minute into aprecipitation flask containing 650 ml of a 4 percent by weight aqueousgelatin solution to which at 50C an aqueous solution of ammonia wasadded in order to obtain a pH-value of 9.3. During precipitation of thesilver bromide the pAg-value was adjusted to and maintained at a valuecorresponding to an E.M.F. of +20 mV (Ag/saturated reference calomelelectrode).

Subsequently, the internal ripening was effected. For that purpose, 3.5ml of a 10 molar solution of formamidine sulphinic acid were added andthe emulsion digested for 30 minutes at 50C. Then the pH was lowered to6.5 and 1.5 ml of an aqueous 0.08 percent by weight solution ofgold(lII) chloride and 1.5 ml of aqueous 2 percent by weight solution ofammonium thiocyanate were added. After said addition the digestion wascontinued for 10 minutes at 50C.

The precipitation was then continued (second precipitation) as followsan aqueous solution of ammonia was added to obtain a pH value of 9.3whereupon 665 ml of an aqueous 3N potassium bromide solution and 665 mlof an aqueous 3N silver nitrate solution were introduced at a rate of 19ml per minute. During precipitation the pAg value was maintained at avalue corresponding to an E.M.F. of 20 mV (Ag/saturated calomelelectrode). The emulsion was solidified after the addition of 234 g ofgelatin was washed in the usual way.

After washing, the pAg was again adjusted to a value corresponding to anE.M.F. of 20 mV (Ag/saturated calomel electrode) and the pH of theemulsion was adjusted to 6.5.

The external fogging of the composite silver bromide granules formed wasthen carried out for minutes at 55C with 9 ml of a 10' molar aqueoussolution of formamidine sulphinic acid per kg emulsion, containing 1 10g of silver bromide and 80 g of. gelatin.

After the fogging treatment, the emulsion was divided into severalaliquot portions. To each portion, were then added per kg 1 g of saponinas coating aid and one of the selenium compounds listed in the table.below in the amount given. Just before coating 500 mg 120 sec. at 20Cin a developing bath having the composition given in example 1.

The sensitometric results obtained with freshly prepared materials andwith materials stored for 36 hours at 57C and 34 percent of relativehumidity are listed in the table hereinafter.

In this table, the speed (S) is expressed on a percentage basis withrespect to freshly prepared reference emulsions, which comprise noselenium compounds and for which arbitrarily a total speed of 100 isgiven.

The density in the exposed areas (minimum density) is a measure of thebrightness of the whites and is denoted in the table by D Weclaim:

l. A direct-positive photographic element comprising uniformly foggedradiation-sensitive silver halide and a selenium compound correspondingto the following formula:

R Se Q 10 karyl group, an aryl group or a heterocycle,

stands for Se-R' or -S-R' wherein R stands for an alkyl group, anaralkyl group, an alkaryl group, an aryl group or a heterocycle;halogen;

In the table are also given the maximum density ob- CN n H tained withfreshly prepared material (D as well as 15 the silver bromide contentper sq.m' of the materials examined. R.

TABLE Fresh material Stored material G AgBrl Selenium compound per kg.emulsion Dmi... Gamma S D.,.;.. Gamma S Dam, sq. m. Nonc 0- 01 5- 05 1000. 01 5. 25 98 3. 24 6. 54 5 ing. of compound 6 0. 01 4. S0 120 0. 014.65 123 3. 50 6.66 5 mg. 01' compound 14 0. 01 4. 45 132 0. 01 4.70 1203.50 6. 73 None 0. 01 4. 80 100 0- 01 5. 10 06 3. 44 6. 68 5 mg. ofcompound 10.. 0.01 4.90 138 0.01 4.80 138 3.44 6.53 5 mg. of compound 110. 01 4.62 138 0- 01 4.60 138 3.44 6. 69 5 mg. of compound 13 0- 01 4.80 135 0- 01 4. 70 135 3. 52 6.90 None 0- 01 5. 35 100 0. 01 5. 05 1053. 48 7. 08 5 mg. of compound 3- 0. 01 5. 142 0.01 5.08 134 3. 56 7. 265 mg. of compound 4-. 0.01 4. B0 195 0.01 5.10 200 3.50 6.75 5 mg. ofcompound 5-- 0. 01 5. 10 158 0. 01 5. 25 166 3. 52 6. 95 5 mg. ofcompound 12 0.01 5.46 170 0.01 5.00 170 3.62 7.01 5 mg. of compound 250. 01 5.05 200 0. 01 4. S5 209 3.64 6. 87 None 0. 01 5.10 100 0. 01 5.30 100 3. 68 7.02 15 mg. of compound 20.- 0. 01 5.35 309 0. 01 5. 50 4003. 52 6. 78 15 mg. of compound 21.- 0. 01 5. 55 204 0. 01 4. 75 204 3.54 6 92 15 mg. of compound 22.. 0. 01 5.30 135 0.01 5. 45 141 3. 60 6.78 15 mg. of compound 23-. 0.01 5.10 145 0. 01 5.10 155 3. 48 6. 59 15mg. of compound 24 0. 01 5. 00 141 0. 01 5. 141 3. 52 6. 68 15 mg. ofcompound 26 0.01 5.35 128 0. 01 5.25 128 3. 50 6.52

None 0- 01 5. 20 100 0. 01 4- 90 105 3. 76 7. 45 15 mg. of compound 280. 01 4. 80 186 0. 01 4. 60 195 3. 46 6. 93

EXAMPLE 4 wherein each of R,, R, and R stands for alkyl, aralkyl Thesensitometric results obtained are listed in the table below.

use.

or aryl and X- stands for an anion but does not exist when R itselfcontains an anionic group, said selenium compound being present in anamount sufficient to increase the speed of said direct-positive element.

2. A direct-positive photographic element according to claim 1, whereinthe said selenium compound is Fresh material Stored material G AgBr/Selenium compound per kg. emulsion Dmin. Gamma S Dmh.v Gamma S Du... sq.m None 0.01 5.37 100 0. 01 5.30 107 3. 48 6. 54 5 mg. of compound 6 0.01 4. 52 132 0. 01 4.35 128 3. 62 6. 66 5 mg. of compound 14 0. 01 5. 25252 0. 01 5. 00 240 3. 58 6. 73 None 0. 01 4. 85 100 O. 01 4. 90 105 3.46 i1. 68 6 mg. of compound 10.. 0.01 4.50 257 0.01 4. 25 234 3.28 0. 535 mg. of compound 11 0. 01 5. 33 182 0.01 4. 45 170 3. 6. 00 5 mg. ofcompound 13 0. 01 4.52 170 0. 01 4. 00 162 3. 6. 00 None- 0- 01 5- 10100 0. 01 4. 80 0B 3. 73 7. 0H 5 mg. of compound 3. 0. 01 4. 70 170 0.01 4. 30 184 3. 72 7. 20 5 mg. of compound 4 0.01 4. 95 288 0. 01 4.90302 3. 68 6. 75

5 mg. of compound 5 0. 01 5. 40 214 0. 01 5. O0 204 3. 64 6. 05 5 mg. ofcompound 12 0.01 5.56 220 0.01 4. 214 3. 84 7. 01 5mg. 01 compound 25 0.01 4. 70 400 0.01 4.50 363 3. 76 0. 87

None 0. 01 5. 05 100 0. 01 5. 35 105 3. 80 7. 0 15 mg. of compound 21]0.01 5. 05 675 0.01 5. 15 740 3.68 6. 78 15 mg. of compound 21. 0. 01 5.35 295 0. 01 4. 40 282 3. 66 6. 92 15 mg. of compound 22 0. 01 4.85 1620. 01 5.15 178 3. 60 6. 7 15 mg. of compound 23 0. 01 4. 178 0. 01 4. 75186 3. 54 6. 5 15 mg. of compound 24. 0.01 4.80 162 0. 01 5.00 162 3. 646. 68 15 mg. of compound 26 0. 01 5. 15 148 0. 01 5. 20 144 3. 62 6. 52

None 0. 5. 25 0. 01 5. 15 102 3. 74 7. 45 15 mg. of compound 28 0.014.90 214 0.01 4.75 204 3. 50 6. 93

present in an amount of from about 1 mg 100 mg per mole of silverhalide.

3. A direct-positive photographic element according to claim 1, whereinthe silver halide has been uniformly fogged by chemical means.

4. A direct-positive photographic element according to claim 3, whereinthe silver halide has been uniformly fogged by means of reducing agents.

5. A direct-positive photographic element according to claim 1, whereinthe fogged silver halide emulsion comprises silver halide grains havingan interior core of silver halide comprising centers promoting thedeposition of photolytic silver and an outer shell of silver halide.

6. A direct-positive photographic element according to claim 5, whereinthe said centers are formed by chemical sensitization of the interiorcore of silver halide.

7. A direct-positive photographic element according to claim 6, whereinsaid centers are formed by treatment of the interior core of silverhalide with a reduction sensitizer and/or noble metal compound.

8. A direcbpositive photographic element according to claim 7, whereinsaid centers are formed by treatment with a reduction sensitizer and agold sensitizer.

9. A direct-positive photographic element according to claim 8, whereinfogging of the silver halide emulsion comprising silver halide grainshaving an interior core of chemically sensitized silver halide and anouter shell of silver halide, is effected by treatment with a reductionsensitizer.

10. A direct-positive element according to claim 9, wherein thereduction sensitizer used in the chemical sensitization of the silverhalide core is the same as the reduction sensitizer used for fogging thesilver halide emulsion.

the silver halide of the outer shell is silver bromide.

13. A direct-positive photographic element according to claim 2, whereinsaid selenium compound is @SeCN.

14. A direct-positive photographic element according to claim 2, whereinsaid selenium compound is 15. A direct-positive photographic elementaccording to claim 2, wherein said selenium compound is 16. Adirect-positive photographic element according to claim 2, wherein saidselenium compound is 17. A direct-positive photographic elementaccording to claim 2, wherein said selenium compound is

1. A direct-positive photographic element comprising uniformly foggedradiation-sensitive silver halide and a selenium compound correspondingto the following formula: R - Se - Q wherein: R stands for an alkylgroup, an aralkyl group, an alkaryl group, an aryl group or aheterocycle, Q stands for -Se-R'' or -S-R'' wherein R'' stands for analkyl group, an aralkyl group, an alkaryl group, an aryl group or aheterocycle; halogen; -CN or wherein each of R1, R2 and R3 stands foralkyl, aralkyl or aryl and X stands for an anion but does not exist whenR itself contains an anionic group, said selenium compound being presentin an amount sufficient to increase the speed of said direct-positiveelement.
 2. A direct-positive photographic element according to claim 1,wherein the said selenium compound is present in an amount of from about1 mg - 100 mg per mole of silver halide.
 3. A direct-positivephotographic element according to claim 1, wherein the silver halide hasbeen uniformly fogged by chemical means.
 4. A direct-positivephotographic element according to claim 3, wherein the silver halide hasbeen uniformly fogged by means of reducing agents.
 5. A direct-positivephotographic element according to claim 1, wherein the fogged silverhalide emulsion comprises silver halide grains having an interior coreof silver halide comprising centers promoting the deposition ofphotolytic silver and an outer shell of silver halide.
 6. Adirect-positive photographic element according to claim 5, wherein thesaid centers are formed by chemical sensitization of the interior coreof silver halide.
 7. A direct-positive photographic element according toclaim 6, wherein said centers are formed by treatment of the interiorcore of silver halide with a reduction sensitizer and/or noble metalcompound.
 8. A direct-positive photographic element according to claim7, wherein said centers are formed by treatment with a reductionsensitizer and a gold sensitizer.
 9. A direct-positive photographicelement according to claim 8, wherein fogging of the silver halideemulsion comprising silver halide grains having an interior core ofchemically sensitized silver halide and an outer shell of silver halide,is effected by treatment with a reduction sensitizer.
 10. Adirect-positive element according to claim 9, wherein the reductionsensitizer used in the chemical sensitization of the silver halide coreis the same as the reduction sensitizer used for fogging the silverhalide emulsion.
 11. A direct-positive element according to claim 10,wherein said reduction sensitizer is thiourea dioxide.
 12. Adirect-positive element according to claim 5, wherein the silver halideof the interior core as well as the silver halide of the outer shell issilver bromide.
 13. A direct-positive photographic element according toclaim 2, wherein said selenium compound is
 14. A direct-positivephotographic element according to claim 2, wherein said seleniumcompound is
 15. A direct-positive photographic element according toclaim 2, wherein said selenium compound is
 16. A direct-positivephotographic element according to claim 2, wherein said seleniumcompound is